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International Journal of Mechanical and Materials Engineering IJMME, Vol.6 2011, No.2, 260-268
EXPERIMENTAL ANALYSIS OF AN INSTRUMENTED CHARPY IMPACT USING STATISTICAL STUDY BASED DATA ANALYSIS
M. B. Ali, S. Abdullah, M.Z. Nuawi, M.M. Padzi and K.A. Zakaria
Department of Mechanical and Materials Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, MALAYSIA.
Email: bas2010eng.ukm.myabgbasyahoo.com Received 25 October 2010, Accepted 28 July 2011
ABSTRACT The dynamic fracture initiation toughness and the
characteristics are evaluated by using the instrumented charpy impact testing.
The standard charpy impact machine is experimentally studied using the relevant data
acquisition system in order to obtain the impact response. Strain gauges were connected to the data acquisition set
and it was then attached to the charpy striker for the signal collection. Aluminium 6061 and low carbon steel
1050 were used in this testing. In this work, statistical based analysis has been performed using I-kaz method.
In addition the power spectrum density PSD approach was then used for the energy based observation and a
signal was converted from the time domain to the frequency domain using the fast Fourier transform FFT
method. Comparison between experimental findings with related parameters such as of different materials, strain
signals pattern, PSD and I-kaz, were finally correlated and discussed. It was found that the modulus of elasticity
was related to the energy absorbed, strain signals amplitude, I-kaz coefficients and PSD. Finally, it is
suggested that the properties of materials and the impact signals pattern is suitable to be analysed using the signal
processing approach. Keywords
: Charpy Impact, I-Kaz, PSD, signal and strain Nomenclatures
E Young Modulus GPa
ρ Density kgm
3
υ Poisson’s ratio
Z
∞
I-kaz coefficient Kurtosis values of signal in low frequency
K
H
Kurtosis values of signal in high frequency K
V
Kurtosis values of signal in very high frequency s
L
, Standard deviation of signal in low frequency
s
H
Standard deviation of signal in high frequency s
V
Standard deviation of signal in very high frequency
P
xx
Power spectrum function of ω r
xx
Autocorrelation function of τ Gjω Frequency spectrum
y Beam deflection
p Angular frequency of vibration
A cross-section of the striker arm m
2
l length of striker m
J mass moment of inertia
ω natural frequency
I moment of inertia
1. INTRODUCTION The charpy v-notch test is a standardised high strain rate
test that can measure the amount of energy absorbed in a material. The absorbed energy using dial system is
considered as a measurement of the material toughness and also as a tool for the ductile-brittle transition
depending on the testing temperature Jang et al., 2008; Ali et al., 2011. The use of instrumented charpy impact
apparatus with the load-time recording system is to determine the fracture energy and the general yielding of
material, the maximum load applied on to the specimens, and finally the moment level of brittle fracture
occurrence Rossol et al., 2002; Kondrakov et al., 2005; Jang et al., 2008.
The dynamic responses of standard charpy impact machine were experimentally studied using strain gauges
and accelerometer that is attached to the impact striker and the results was then validated with finite element
analysis Shterenlikht et al., 2005. It was showed the first natural frequencies of the charpy sample have high
modal magnitudes in the acceleration signal but different with strain gauges. An effect of the striker shape and
position of strain gauge on instrumented charpy impact test was also studied by Toshiro et al. 2000. The result
illustrates the effect of the hammer vibration appeared to be stronger around the end of the slit. Sahraoui and
Laitailate 1998 explained the different materials with the contact stiffness that can be found for striker and the
specimen. In addition, the interaction between the striker and the specimen play a dominant role towards the effect
of vibration and impact using the specific method to evaluate the load oscillation frequency. Furthermore,
Kondryakov et al. 2005 studied a multichannel system of high-speed strains and loads recording process during
the fracture toughness testing, with strain gauges attached to the striker and also to the specimen support. Thus, the
information of the specimen deformation during the test can be recorded.
The content of this paper focuses on the aluminium 6061 material as this kind of material is widely used in many
engineering structural application. The aluminium 6061 alloy is a heat treatable, type of wrought Al
–Mg–Si alloy, in which magnesium and silicon are added either in
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balanced amounts to form quasi-binary Al –Mg
2
Si or with an excess of silicon needed to form Mg
2
Si precipitate. This alloy contains 0.2 Cr, which provides an
improved corrosion resistance. While the presence of the excess silicon improves age hardening response, it may
however reduce the ductility and cause intergranular embrittlement, due to the segregation of excess silicon to
grain boundaries. Aluminium 6061 alloy has superior mechanical properties such as a high strengthweight
ratio, excellent weld ability and deformability, it is considered for use in many advanced applications where
the structural components are subjected to dynamic loading Toh Kanno, 2004; Jogi et al., 2008,
Anilkumar et al., 2011, Prabhu et al., 2011. This study focuses on the aluminium 6061 alloy as the fabricated
rim material as the rim system of the vehicle directly experiences the impact of the load when the vehicle is
driven on the road. It is estimated that more than half the cars on the road today ride on alloy rims and the
popularity of this wheel style is hard to top for a number of reasons, but there are some potential pitfalls to watch
out when an alloy is selected Research Activity 2009, Ali et al., 2011. Vehicle wheels have to be considered in
particular due to their beneficial effect such as safety, comfort and energy saving. As a safety-related
component, the essential factors in wheel applications are the fatigue strength and the impact strength Qiang et al.,
2010. The wheel design and development departments conduct three main wheel tests the rotating bending test,
the radial fatigue test and the impact test to test a prototype wheel for various fatigue and durability
considerations. The impact test is established to evaluate the impact damage on the wheel when the wheel hits a
curb Chang and Yang, 2009. The velocities when a wheel hits a curb are variables that depend on the speed
of the car. The velocity v
= 5.18 ms that is similar to the instrument charpy impact machine need to be studied.
Unlike other type of wheels that are normally made of heavy and very durable steel, alloy rims comprise of
aluminium, magnesium or a combination of both metals. These metals are advantageous due to them being light-
weight,
corrosion resistant,
have high
thermal conductivity and possess the characteristics of casting.
While alloy wheels have their advantages, there are however, some disadvantageous in using them too. One
of the problems that arise with this alloy is the reduction in its durability. It is undeniable that steel is an extremely
durable material, but aluminium is not. Thus alloy rims that are fabricated using aluminium 6061 are easily
damaged fractured easily and can even be destroyed. This disadvantage create problem for drivers who find
out later that they have to replace their vehicle rims or pay for a potential costly repair. What the facing now
almost all wheel makers in this country not implement design analysis and do not have capability and only
involve physical test. To identify all the potential failure and to optimize the design in order to reduce the failure
on rim alloy wheel material need to be study Research Activity 2009, Cerit, 2010, Ali et al., 2011. From the
literature the review, less study were found in related area especially on failure mode by means of impact
loading using a signal processing approach. Detail research using signal processing approach need to
investigate which material aluminium 6061 and carbon steel 1050 is tougher and more safety with longer energy
absorbing. From this problem statement the main scope of this paper is to identify and to analyse the impact
analysis of the alloy rim material using signal processing approach.
To achieve the goal of this study, the analysis will be performed using the statistical analysis, which is a new
statistical based method which is known as Integrated Kurtosis-based Algorithm for Z filter I-kaz technique.
The I-kaz method calculates the related coefficient for the measured impact signal. The input data of I-kaz
method was the impact signal which was obtained from the experimental work. The impact signal was monitored
by the value of the I-kaz coefficient, Z
∞
and three dimensional
graphic display
of the
magnitude distribution Nuawi, 2007; Abdullah et al., 2009. In
addition, the vibration energy distribution is another method used to clarify the behaviour, by means of the
power spectral density PSD analysis. The expected result the properties of materials and the impact signals
pattern is suitable to be analysed using the signal processing approach.
2. METHODOLOGIES The materials used for impact specimen are aluminium
